Generator voltage increases when load applied.

[asherwin]

I have the built in Onan 5500 gennie. It has worked flawlessly for five years. Hours are fairly low at less than 100. I have a Camco AC meter which I leave plugged in all the time. This helps me know when shore voltage is weak especially when using 30A service in some parks. Typically voltage will decrease when a load is applied such as A/C, microwave, coffee maker etc. I would see the same decrease in voltage whether on shore power or using gennie. Recently when using gennie the voltage reading will increase when a load is applied. Can someone help me understand why this is happening? Thx.

 

[porthole]

[SUP]Increasing how much?

Voltage output is set by RPM, so depending on how high it is going, you might have a governor issue.
Do you have the manual?
Did you check for fault codes?[/SUP]

 

[asherwin]

Voltage increases 2-6V when single appliance load applied which is usual decrease. No faults indicated on gennie display.

 

[porthole]

Voltage increases 2-6V when single appliance load applied which is usual decrease. No faults indicated on gennie display.

What is the voltage increasing to?

With the genset a slight increase is not unusual. When you are on shore power you have a limited set amount of power available, whatever is in the pedestal.
Add loads, voltage may drop.

When using the genset, adding loads will slow the gen down and the governor will bring it back up to speed, and typically you may see a slight voltage increase, not decrease.

The fault codes are not read at the gen display. They are a series of flashes at the breaker panel on the generator.

Do you have the manuals?

If not pm me your email and I will forward you PDF copies of the user and repair manuals.

 

[asherwin]

Thanks for the input. I have the manual. There are no fault codes flashing. When load applied the voltage will increase for the duration of the applied load. Base voltage (no load) can range from 105V to 120V depending on quality of shore power. Increase in voltage will be 2-6V over base dependent on specific appliance load. Eg. A/C would be greater increase than say microwave.

 

[avvidclif]

That's not making any sense. "Generator voltage will increase depending on value of shore power". With no shore power, generator only, what is the voltage? When load applied on generator what is the voltage? MeThinks you are trying to compare an apple to an orange.

 

[LBR]

You mentioned nothing about trying anything other than relying on your trusty old standby....try testing voltage with a VOM.

 

[asherwin]

That's not making any sense. "Generator voltage will increase depending on value of shore power". With no shore power, generator only, what is the voltage? When load applied on generator what is the voltage? MeThinks you are trying to compare an apple to an orange.

Here is example. Genni output voltage with no load is 120V. With load applied eg. Microwave, voltage output increases to 123V.

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You mentioned nothing about trying anything other than relying on your trusty old standby....try testing voltage with a VOM.

Trusty AC meter works as expected when on shore power showing decrease in voltage when load applied. When on gennie power meter shows increase in voltage when load applied.

 

[fritzwell]

Here is example. Genni output voltage with no load is 120V. With load applied eg. Microwave, voltage output increases to 123V.

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Trusty AC meter works as expected when on shore power showing decrease in voltage when load applied. When on gennie power meter shows increase in voltage when load applied.

The power source is prolly miles away from the rv park your at and thr whole park is on that source. Your on your generator which is only a few feet away and your load is the only thing on it. Sounds to me like you've got a good generator. Hit that gen with more load and you'll most likely see what your looking for.
Fritz

 

[danemayer]

Some info

What the Regulator DoesWhen the generator is first started, the regulator receives the field flash voltage from the control board and applies it to the generator field (rotor) to initiate AC voltage buildup in the stator. After the generator output voltage builds up, the regulator maintains it nearly constant (within a few volts of 120 VAC) under conditions of varying load. It does this by sensing the 120 volts and constantly adjusting the DC field (rotor) voltage up or down, as needed. For example, if you turn on a light, the regulator would respond by increasing the field voltage only slightly to compensate for the added load. If you turn on a microwave oven or an air conditioner, the regulator would increase the field voltage by a much larger amount, in proportion to the heavier load. The regulator has a built-in protection circuit that reduces the output voltage of the generator if the engine is running too slow. The purpose of this feature is to protect your appliances from receiving full voltage at the lowered frequency, as this can cause damage to motors and transformers.

and

Q. The voltage at the AC outlet is too high (above 125 VAC at no load) on start up, or gradually climbs after the generator has been running for a while. What causes this?A. If the voltage is somewhat high or climbs, the regulator is defective and needs to be replaced. If the voltage immediately goes to 160 VAC on start-up, the problem is either the regulator or a loose connection at pin 2 of the regulator. Check connections before replacing the regulator.

and

Q. Is there a place where I can easily check for the proper voltages when the generator is running?A. Yes. The 120 VAC and/or 60 Hz frequency can be checked between pins 2 and 3 of the regulator or at any outlet, and should be between 117 and 126 VAC at no load. The field voltage can be checked between pins 9 and 10 of the regulator and should be 35-40 volts at no load and rise to about 60 volts at full load.

There can be causes of voltage problems downstream from the generator - like a loose connection in the transfer switch.

 

[CDN]

[SUP]Increasing how much?

Voltage output is set by RPM, so depending on how high it is going, you might have a governor issue.
Do you have the manual?
Did you check for fault codes?[/SUP]

Actually voltage does not increase when the generator speeds up, in this case has to be the same speed no matter what the load is The Speed change in the engine would mean the frequency would change from 60 hz. The actual alternator is not efficient at anything but the proper speed it is designed for. A Onan is not a inverter style generator, speed must stay constant.

As far as the OP the regulation of the generator voltage is a the issues. 2 or 3 volts is no big deal. Depending on the generator the output waveform might change under heavy load causing a metering error due to how the meter makes DC out of AC internally. I would check with a better meter to make sure. Then as dan stated you can look further at the actual generator itself.

 

[asherwin]

Thanks everyone. I now have a couple of leads to follow.

 

[porthole]

Actually voltage does not increase when the generator speeds up, in this case has to be the same speed no matter what the load is The Speed change in the engine would mean the frequency would change from 60 hz. The actual alternator is not efficient at anything but the proper speed it is designed for. A Onan is not a inverter style generator, speed must stay constant.

As far as the OP the regulation of the generator voltage is a the issues. 2 or 3 volts is no big deal. Depending on the generator the output waveform might change under heavy load causing a metering error due to how the meter makes DC out of AC internally. I would check with a better meter to make sure. Then as dan stated you can look further at the actual generator itself.

Ah yup the frequency changes with the speed. The voltage is controlled by the field through the controller. And it looks like a fault code isn't thrown until the output reaches about 125 volts.